“尤特”强降水过程大气层结分析

Analysis of the Atmospheric Stratification During the Intense Rainfall of Severe Typhoon Utor

1311号强台风"尤特"登陆后给广东带来持续性大范围强降水,对流降水特征显著。分析了"尤特"影响期间大尺度环流背景,重点讨论了此次持续性强降水过程中大气层结问题。发现低空急流向广东输送强的暖平流,是广东大气层结不稳定得以持续维持的根本原因。进一步分析发现,低空急流本身并不是"暖"的,当"尤特"趋向陆地时,陆地上的暖气团在"尤特"环流强迫下向南传播扩散,低空急流穿越这一暖区时温度升高才具备"暖"的特性。这一事实在以前并未被关注到。通过个例反查,在许多登陆后造成连续强降水的台风过程中均发现了这一特征。因此,台风登陆引起环境温度场的演变以及与低空急流的配置需引起重视。

After the landfall of Utor, a severe typhoon in 2013 （coded 1311 ）, a sustained, large-scale rain appeared in Guangdong province, which was much convective. In this work, the large-scale background is studied for the duration of Utor with the focus on the atmospheric stratification during the rain, It was dis- covered that a warm advection transported to the province by a low-level jet stream was the fundamental cause for the maintenance of unstable atmospheric stratification. Further analysis found that the low-level jet stream was not warm in nature but became warm when it passed a warm airmass over land which was forced to spread southward with the forcing of the typhoon as it approached the coast. It has never been observed before and the phenomenon repeats itself in other cases of landfalling typhoons causing sustained heavy rain. Attention should be drawn to the fact that the landfall of typhoons results in the evolution of ambient tempera- ture fields and their allocation of low-level jet streams.